[Qt-creator] Does someone understand this CMake error

[Nikos Chantziaras]

This is with Qt Creator 4.5.0 beta1 on Linux (Gentoo AMD64.)
GCC 6.4.0
CMake 3.9.4
Ninja 1.8.2

In the below, "foo" is your bog-standard add_executable() target:

   error: The install of the foo target requires changing an RPATH from
   the build tree, but this is not supported with the Ninja generator
   unless on an ELF-based platform.  The CMAKE_BUILD_WITH_INSTALL_RPATH
   variable may be set to avoid this relinking step. CMakeLists.txt:191
   (include)

I *am* on an ELF-based system (Linux 64-bit.) I can build the project 
manually outside of Creator just fine:

   $ mkdir build && cd build
   $ cmake -DCMAKE_GENERATOR=Ninja ../
   $ ninja

Builds fine.